In recent years, federal administrative regulations have required increasingly stringent standards for the cleanup of air from manufacturing operations, such as the textile fiber preparation operation, in which considerable quantities of lint and dust are generated to the extent that conventional equipment no longer satisfies such regulations. For example, some regulations require that the cleanup be of such efficiency that the return air contains no more than 200 micrograms of contaminants per cubic meter. The reason that such conventional equipment is unsatisfactory is because that cleanup of the contaminated air stream is generally attempted in a single or two stage operation. It is practically impossible to provide such a device which will collect the long fibers, as well as the minute dust particles simultaneously without clogging so fast as to create a significant back pressure on the incoming contaminated air stream.
Some efforts have been made to employ a multistage filter, which efforts have used either a cyclone device or a partial cyclone device upstream from a rotary drum filter to remove the heavy contaminants prior to introduction to the rotary drum filter, which may become quickly clogged with heavy particles. See, for example the U.S. Patent to Baigas No. 3,864,107. These efforts are expensive in that the parts for the two stages cannot be standardized, and further may require considerable expensive floor space in the manufacturing plant.